Photogrammetry

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Route points placed at the same height relative to the ground. This height is calculated based on camera settings and set GSD value. Calculated parameters (number of passes, number of camera shots, etc.) are displayed in route log window (see Figure 4, 13). Photogrammetry tool is available for UgCS ONE, UgCS PRO and UgCS ENTERPRISE licence.

Note: Photogrammetry tool requires selected camera as a payload. The camera must have properly specified (positive) values of focal distance, sensor size (width and height), and sensor resolution (horizontal and vertical).

Additionally to all common options, these features are available for Photogrammetry tool:
Move / Rotate segment - select+hold the blue circle in center to drag-and-drop Area scan segment to other location. Select+hold circle’s rim to rotate whole segment.
Camera - payload assigned to a profile. In case of multiple cameras assigned to profile it is possible to select which camera to use.
Ground resolution (GSD, cm) – approximate ground resolution for resulting images (in centimeters per pixel).
Forward overlap (%) – ratio of the overlap in neighboring frames (consecutive by motion vector, see the scheme below). Value is set in the range from 1% to 90%.
Side overlap (%) – ratio of the overlap in neighboring frames (placed in neighboring rows, see the scheme below). Value is set in the range from 1% to 90%.
Camera top facing forward – concerns the camera orientation to the motion vector. The flag assumes the camera is oriented so that the frames overlap over the upper frame boundary motion vector. If the flag removed, the frames overlap along the lateral frame boundary.
Direction angle - used to change the direction of the main scanning progress. By default, the algorithm calculates a route scan in a bounded polygon so that the main course of the scan performs in the direction of "South-North".
Additional waypoints – if the flag cleared, the algorithm generates only the turning points. If the flag is set, additional waypoints for camera shooting will be generated depending on overlap and camera settings.
Overshoot (m) – adds extra segment to both ends of each survey line to enable extra space for turns.
'Overshoot speed (m/s) - option to decrease/increase vehicle speed for overshoot segment while passing turns.
Altitude type AMSL or AGL to set Flight height.
Altitude AMSL - calculated from lowest point using GSD. However, the number of shots required to meet forward overlap and side overlap constraints are being calculated using altitude difference between calculated flight altitude AMSL and highest point of the area.
Allow partial calculation option to allow route calculation in these cases:
a. The part of route exceeds maximum AMSL of route
b. Relief height is unavailable at some point(s) of route
c. The part of route exceeds the maximum fence radius
d. The part of route in No-fly zone (NFZ)
No action at last point – remove action for last waypoint.

Note: For those pilots who use autopilot that supports camera triggering by distance or time, there is automated algorithm that calculates and sets the correct parameters. It is not necessary to use this approach with Actions in every point parameter.



Sample photogrammetry route



where 'fo' - forward overlap, 'so' – side overlap
Calculation:
1. Calculate the altitude required for camera recording:
a. heightAgl = ( f * GSD * sensorWidthPx ) / sensorWidth;
b. heightAgl = ( f * GSD * sensorHeightPx ) / sensorHeight;
c. Selected minimum value calculated of heightAgl.
2. Calculate the frame size:
a. frameWidth = ( sensorWidth * heightAgl ) / f;
b. frameHeight = ( sensorHeight * heightAgl ) / f.

where 'f' is True focal distance
The scanning area is partitioned into frames of calculated sizes with given overlaps. The direction of passage is selected using Direction angle. The route is is formed as 'snake'..
AGL Tolerance (m) – enables to fly straight trajectories over slightly waved landscape, by specifying how precisely the UAV should follow required altitude above ground. To maintain specified height additional waypoints will be added if difference of height is larger than AGL tolerance. The smaller AGL tolerance value, the more amount of waypoints will be generated. If AGL tolerance is set 0 (zero) UAV’s altitude will be constant throughout route, but many additional waypoints will be added.
No action at last point removes action for last waypoint.
Double grid - if enabled, adds a second grid to the survey are in a 90-degree angle according to first grid.